The subject matter disclosed herein relates to heating, ventilation and air conditioning (HVAC) systems. More specifically, the subject matter disclosed herein relates to evaporators for HVAC systems.
HVAC systems, such as chillers, use an evaporator to facilitate a thermal energy exchange between a refrigerant in the evaporator and a medium flowing in a number of evaporator tubes positioned in the evaporator. In a flooded evaporator, the tubes are submerged in a pool of refrigerant. In the flooded evaporator system, compressor guide vanes and system metering tools control a total rate of refrigerant circulation through the system. The specific requirement of maintaining an adequate refrigerant level in the pool is achieved by merely maintaining a level of charge, or total volume of refrigerant in the system.
Another type of evaporator used in chiller systems is a falling film evaporator. In a falling film evaporator, bundles or groups of evaporator tubes are positioned typically below a distribution manifold from which refrigerant is urged, forming a “falling film” on the evaporator tubes. The falling film terminates in a refrigerant pool at a bottom of the falling film evaporator. In normal typical evaporator construction, the evaporator tubes are supported by a number of support sheets spaced along the length of the tubes, while a baffle is installed around a suction nozzle to protect the compressor from entrained liquid droplets. This baffle effectively blocks upward vapor flow below the baffle, in a section bounded by two support sheets nearest the suction nozzle. To compensate for this blockage, a large vertical gap, on the order of 6-7 inches, is left between the top edges of the support sheets and the bottom face of the baffle to redistribute upward vapor flow around the baffle. This large gap translates into undesired increased height of the evaporator, and is less than optimal in increasing the uniformity of upward vapor flow.